Polymers for Synthesis of Nanoparticles

Controlled release biodegradable nanoparticles for clinical applications can be made from a wide variety of polymers, including poly(lactic acid) (PLA),93 poly(glycolic acid) (PGA), PLGA,94 poly(orthoesters),95 poly(caprolactone),96 poly(butyl cyanoacrylate),97 polyanhydrides,98 and poly-N-isopropylacrylamide.99 Although many fabrication methods exist, polymeric nanoparticles are frequently made using an oil-in-water emulsion,18,100 which involves dissolving a polymer and drug in an organic solvent, such as methylene chloride, ethyl acetate, or acetone. The organic phase is mixed with an aqueous phase by vortexing and sonicating and then evaporated, forcing the polymer to precipitate as nanoparticles in the aqueous phase. The particles are then recovered by centrifugation and lyophilization.

One of the considerations with respect to the material used for drug delivery is its ability to encapsulate drugs as well as degrade over the appropriate times. This subject has been an active area of investigation by our group and other investigators in academic and industry laboratories for several decades. The result has been an increasing arsenal of polymers with distinct encapsulation and release characteristics for a myriad of research, industrial, and clinical applications.101,102 PGA and PLA are common biocompatible polymers that are used for many biomedical applications. PGA is hydrophilic because it lacks a methyl group and is more susceptible to hydrolysis, making this polymer easily degradable. Alternatively, PLA is relatively more stable in the body.103 Through these unique properties, polymers such as PLGA have been derived that are made from both glycolic acid and lactic acid components. The ability to change the ratio of these two components of the polymer can then be used to dramatically alter the rate of degradation. Therefore, by choosing the desired polymer system for the synthesis of nanoparticles the rate of degradation and subsequent release of the molecule may be tuned for the intended application.

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